Flow swirl impact at the rocket engine nozzle inlet on the flow coefficient

DOI: 10.34759/vst-2021-2-142-151

Аuthors

Shaydullin R. A.^*, Bekerov A. R.^**, Sabirzyanov A. N.^***

Kazan National Research Technical University named after A.N. Tupolev, 10, Karl Marks str., Kazan, 420111, Russia

*e-mail: samsankimanki@bk.ru
**e-mail: bekerovdok@gmail.ru
***e-mail: ansabirzyanov@kai.ru

Abstract

The main issue while rocket engine design, particularly the solid propellant rocket engine (SPRE), is ensuring indispensable engine characteristics, during which operation the probability of acoustic instability occurrence at various modes cannot be excluded. Application of various shapes of the solid propellant channel, grooves as well as combustion products flow swirling inside the engine, which, in turn, may both reduce the probability of the acoustic instability occurrence and increase it, facilitates this. The presented article considers the SPRE, which distinctive feature consists in the presence of the controlled flow swirling inside the combustion chamber.

The purpose of the work was studying impact of the swirled flow and various shapes of the classical inlet subsonic sections of the nozzle on the flow coefficient and forming recommendations for their application.

The state-of-the-art techniques of computational aero dynamics were employed for studying the flow coefficient of classical subsonic nozzle sections under the swirled flow impact. Numerical modelling was being performed employing classical models based on averaged Reynolds Navier-Stokes equations (RANS), which ensure optimal relationship between the obtained results accuracy and resource intensiveness. The RNG k— turbulent model with typical set of model constants, able to ensure the required accuracy according to declared goal and adopted assumptions, namely quasi-stationary axisymmetric adiabatic approximation of the ideal-gas formulation was being employed in the presented work.

Geometry of the computational model supposed application of classical subsonic nozzle sectors (bottoms) with variable parameters of the subsonic jet narrowing, inlet section, from which the swirled flow boundary conditions were being set, unchanged geometry of the supersonic part of the nozzle and extra volume behind the nozzle cutoff. The grid quality was being maintained constant when the computational model geometry changing.

Classical bottoms with conical, elliptical and flat shapes of the nozzle subsonic part, as well as the contour designed with Vitoshinsky formula were being studied in this work. The swirled flow intensity, characterized by the Higher-Baer coefficient Sn, was the boundary condition for the combustion products flow at the nozzle subsonic part inlet. The dependencies of the flow coefficient on the swirled flow intensity at various shapes of the nozzle subsonic part were obtained.

The results of flow characteristics of the subsonic sectors contours under study are being compared with each other at the same swirled flow intensity. The article shows that the swirled flow intensity increasing at the nozzle subsonic part inlet up to Sn = 0.4 leads to the flow coefficient decrease by no more than 0.14%. The largest flow coefficient and more uniform velocity profile in the minimum section when the swirled flow feeding corresponds to the Vitoshinsky contour due to the smoother contour to the minimum nozzle section inlet. Recommendations on the parameters of the transitional sector from the cylindrical part of the chamber to the bottom contour and throat section of the inlet to the minimum section for various bottom shapes are presented. Radius of the inlet to the throat section minimum section has the greatest impact on the flow coefficient.

Keywords:

rocket engine, swirled flow intensity, diffuser, gas dynamic component of the flow coefficient

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